Surfactants are used in many chemical reactions, such as for example emulsion polymerization reactions. Emulsion polymerization takes place in a heterogeneous solution which is most often an oil-in-water solution but may also be a water-in-oil solution, or other emulsion type. A monomer (such as for example styrene or methyl methacrylate), a surfactant, and a free radical initiator are added to the emulsion. Polymerization of the monomers occurs within micelles formed by the surfactant and is aided by the free radical initiator molecules.
Microemulsion polymerization forms nano-sized polymer particles. Microemulsions have certain desirable characteristics such as the forming of optically clear colloids and the capability of forming small-sized polymers that can be engineered with a wide range of properties.
Microemulsion polymerization requires a significant amount of surfactant (for example 10% of the total mass) to stabilize the interfacial area. But a high level of surfactant can affect properties of the microemulsion and/or have an affect on biological activity. This can be a problem for example when the microemulsion polymerization product is intended for medical applications.
Microreactors are often used for conducting microemulsion polymerization. The high surface-to-volume ratio of microchannels within microreactors produces dominant surface tension forces which may be advantageous when forming certain microemulsions. Microreactors generally include a network of microchannels (for example micron-sized channels). Chemical agents can be brought together via various microchannels and allowed to react in one or more controlled regions of the microreactor. The sequence of reactions can be controlled so as to produce the desired final product. Electrokinetically driven microreactors employ electrodes placed in reservoirs. Voltages can be applied to the electrodes in a specific sequence, often under computer control, to cause the flow of polar liquids using electric fields to bring the reagents together in a desired fashion. Microreactors may also be hydrodynamically driven. Hydrodynamic pumps may be conventional or micro-scale pumps—such as syringe-type pumps—that are either external to the microreactor, or which have small moving parts inside the microreactor.
A ferrofluid is a liquid which becomes strongly polarized in the presence of a magnetic field. A ferrofluid is a magnetic fluid comprised of magnetic particles—in particular nanoparticles—coated with a surfactant and suspended in water or an organic solvent. A ferrofluid is a colloid. The magnetic particles are usually magnetite, which are solid ferrous (iron-based) compounds.